Recently, various portable electric devices, such as mobile phones, personal digital assistant (PDA), and notebook computers have been developed, because of their small size, light weight, and power-efficient operations. Accordingly, flat panel display devices, such as liquid crystal displays (LCDs), plasma display panels (PDPs), field emission displays (FEDs), and vacuum fluorescent displays (VFDs), have been developed. Of these flat panel display devices, the LCDs are currently mass produced because of their simple driving scheme and superior image quality.
The LCD device is a transmissive type display device, and displays a desired image on a screen by controlling an amount of light passing through a liquid crystal layer by a refraction anisotropy of a liquid crystal molecule. Accordingly, the LCD device is provided with a backlight, an optical source passing through a liquid crystal layer for image display. The backlight is generally divided into an edge type backlight that a lamp is installed at a side surface of a liquid crystal panel thus to provide light to a liquid crystal layer, and a direct type backlight that a lamp is installed at a lower portion of a liquid crystal panel thus to directly provide light to a liquid crystal layer.
According to the edge type backlight, a lamp is installed at a side surface of a liquid crystal panel thus to provide light to a liquid crystal layer through a reflector and an optical guide plate. Accordingly, the edge type backlight has a thin thickness thereby to be mainly applied to notebook computers, etc. However, the edge type backlight has the following problems. Since a lamp of the edge type backlight is installed at a side surface of a liquid crystal panel, it is difficult to apply the edge type backlight to a liquid crystal panel of a large area. Also, since light is supplied to the edge type backlight through an optical guide plate, it is difficult to obtain high brightness. Accordingly, the edge type backlight is not proper to be applied to a liquid crystal panel for an LCD television of a large area.
According to the direct type backlight, light emitted from a lamp is directly supplied to a liquid crystal layer. Accordingly, the direct type backlight can be applied to a liquid crystal panel of a large area, and high brightness can be implemented. Therefore, the direct type backlight is mainly used to fabricate a liquid crystal panel for an LCD TV.
FIG. 1 is a view showing a structure of an LCD device having a direct type backlight in accordance with the conventional art.
As shown, the LCD device 1 comprises an LC panel 3, and a backlight 10 installed at a rear surface of the LC panel 3. The LC panel 3 for implementing an image comprises a transparent lower substrate 3a such as glass, an upper substrate 3b, and an LC layer (not shown) formed therebetween. Although not shown, the lower substrate 3a is a thin film transistor (TFT) substrate where a driving device such as a TFT and a pixel electrode are formed, and the upper substrate 3b is a color filter substrate where a color filter layer is formed. A driving circuit unit 5 is provided at a side surface of the lower substrate 3a, and thus applies a signal to the TFT and the pixel electrode formed at the lower substrate 3a, respectively.
The backlight 10 comprises a plurality of lamps 11 for emitting light thereby supplying it to the LC panel 3, a reflector 17 for reflecting light emitted from the lamps 11 thereby enhancing optical efficiency, and an optical sheet 15 for diffusing light emitted from the lamps 11 thereby making it be incident on the LC panel 3.
Typically, a straight-type lamp is used. However, the straight-type lamp has the following problems. As size of the LCD device increases, length of the straight-type lamp and the number of the straight-type lamps have to increase in order to uniformly supply light to the LC panel. Accordingly, fabrication cost for the LCD device is increased.
Recently, a U-shaped lamp is being presented in order to prevent the number of the straight-type lamps from increasing. Since one U-shaped lamp has an electrode at an end portion thereof, it serves as two straight-type lamps. Accordingly, the number of the U-shaped lamps is reduced into a half when compared with the number of the straight-type lamps, and thus fabrication cost is reduced.
FIG. 2 is a view showing a structure of a backlight having a U-shaped lamp in accordance with the conventional art. As shown, the backlight 10 is provided with a plurality of U-shaped lamps 40 on a reflector 17. The U-shaped lamps 40 are supported by supporters 30 installed at both side surfaces of the backlight 10. Although not shown, an optical sheet for enhancing efficiency of light emitted from the U-shaped lamps 40 is arranged on the U-shaped lamps 40.
FIG. 3 is a perspective view showing a part of ‘A’ in FIG. 2, which shows a state that the U-shaped lamps 40 are fixed by the supporters 30. As shown in FIG. 3, the supporter 30 is provided with a plurality of holes 32. A curved portion of the U-shaped lamp 40 is insertingly fixed into the adjacent holes 32 penetratingly formed in the supporter 30. A first electrode 41 and a second electrode 42 are respectively formed at both ends of the U-shaped lamp 40, and emit light by emitting discharge gas filled in the U-shaped lamp 40. Since one U-shaped lamp 40 serves two straight-type lamps, the number of the U-shaped lamps is reduced and thus power of a backlight that occupies most of regions of an LCD device is reduced.
However, the conventional backlight has the following problems. When the U-shaped lamp 40 is turned on, the curved portion thereof that has been inserted into the supporter 30 is not provided with light. Accordingly, the curved portion of the U-shaped lamp 40 has a lower temperature than a central region of the backlight 10. When the lower temperature is maintained for a long time, discharge gas of Hg injected into the U-shaped lamp is concentrated into the curved portion. Accordingly, entire brightness of the U-shaped lamp 40 becomes uneven.